Abstract

Objectives
1. To determine the impact of rock lobster fishing on abalone population dynamics
2. To evaluate the effect of abalone fishing on the community structure of the reef
3. To understand rock lobster predator-prey relationships, particularly in relation to changes
-that may have occurred as a consequence of fishing
Outcomes achieved
Moving -from a single species assessment approach that has been the benchmark in
fisheries globally to an approach that encompasses broader ecosystem issues requires
both new methods and new concepts. This project used the abalone and rock lobster
fisheries in Eastern Tasmania as a laboratory for which to trial new methods that
would underpin an ecosystem approach to fisheries management (EAFM) or
ecosystem based fisheries management (EBFM).
Recent research into the rebuilding dynamics 'of abalone and rock lobster populations
within a marine protected area (MPA) identified the potential for interaction between
these populations. Understanding these interactions was considered important if
management decisions were aimed at` optimising .the benefit from the combined
resource. Demonstrating these interactions was seen as the first step by which to
engage stakeholders so that they could recognise that managing either fishery
separately could impair the productivity of the other fishery.
`
The key observation in the MFA was that the medium size class of abalone was
missing compared to adjacent fished sites. It was considered that the increase in
lobster abundance and size within the MFA was a primary driver for this observation.
Using standard surveys techniques 'we were able to identify that abalone emerge at a
larger size within the MFA and' that this was probably a behavioural response to the
phase. Using a novel approach that linked abalone shell markings to lobster attacks,
we were able to provide further supporting evidence that lobsters were important
predators of abalone and that the abundance and I`arger size of lobsters in the MFA
resulted in higher mortalities.
While the above outcomes indicated that lobsters did predate on abalone, we
undertook a combined stable isotope and fa.tty acid signature approach to evaluate the
importance of abalone to lobster diet. Although this method did detect differences
between diets of rock lobster found in MPAs and fished regions, the contribution of
abalone to the diet was relatively minor. Stable isotopes and fatty acid signatures are
normally obtained from tissue samples to provide information on dietary items
ingested over periods of months, depending. on tissue turnover rates. In contrast, we
evaluated the use of more recent developments in dietary DNA technology to identify
key dietary items that had been ingested over periods of 1""3 days. We were able to
develop a quick and non-lethal technique for extracting samples for dietary DNA
analysis that enabled lobsters to be returned to their place of capture ,(e.g in MPAs) or
to. the fisher for future live export. _DNA markers were developed for specific prey
items such as abalone, the common urchin and the invasive .long $pined urchin.
Aquarium trials have demonstrated that the signal can be detected between 5 and 60
hours after ingestion of the prey item. This allows for dietary information to be
obtained from lobsters that have been captured in traps left on the fishing grounds for
up to 3 days. The DNA dietary method holds considerable promise for-evaluating the
interactions between predators and their prey in marine ecosystems.
Finally, we trialled acoustic telemetry as a method to understand the behavioural
responses of lobsters inside and outside MPAs. There have been very few such
'behavioural studies undertaken on lobster and none that address the effects of fishing
on ecosystem usage. Using the latest technology in acoustic telemetry we were able to
demonstrate that fishing has impacted on lobster behaviour. It ,was also surprising to
find that lobster activity patterns within the MFA demonstrated a degree of
segregation between small and large lobsters of each sex and that these different
activity patterns were not reflected in catchability of lobster in traps.
The second component of this.report was to evaluate the effect of abalone fishing on
inshore reef ecosystems. The first section of this component used fisher's knowledge
to evaluate historical changes. Outcomes from fisher`)s interviews indicated that the
fished area of reefs is dynamic and is affected by a complex relationship between
abalone abundance, the amount of catch to be taken (TAC) and the financial rewards
to abalone divers. Fishers stated that abalone populations fluctuated regionally
although a general trend in more resilient (measured as the observed ability to recover
from fishing) populations were found further south in Tasmania. Divers also noted a
wide range of ecosystem changes that had also occurred over the past 30 years.. Most
divers recognised that the abalone populations that they were fishing had been
_severely depleted Although not consistent across all divers, several identified that
after the removal of abalone, _preferred' abalone habitat changed to _less preferred'
habitat. This was acknowledged as a change from crustose coralline algal (CCA)
dominated habitat to habitat dominated by sessile invertebrates and foliose algae
(IFA),.
Fisher knowledge was also supported by an empirical study of inshore reefs. While
fine scale habitat preferences could not be identified in this study, the regional
'differences noted by fishers were distinguishable. In particular, there was a change in
understory community composition from north to south, although the Acteaons
region in south eastern Tasmania was substantially difference to other sites on the
East Coast.
In conclusion, this project has demonstrated a range of novel and innovative ways to
address species interacHons and paths the way for an improved understanding of the
effects of fishing on ecosystems. Importantly, it showed that a number of factors
ranging from the use of fishers knowledge to the use of recent technological advances
were equally valuable in providing the science necessary to underpin the move
towards an integrated multi.-species approach to fisheries management.